1. Field of the Invention
The present invention relates to a space heater, and more particularly to a space heater having a freeze prevention function to prevent indoor facilities from being frozen.
2. Description of the Related Art
Heretofore, there have been known FF type (forced draft direct vent type) space heaters which supply outdoor air as combustion air to a burner (heating means), burn a fuel in the burner, heat a heat exchanger with exhaust gases from the burner, and then discharge the exhaust gases to the outdoor environment.
When such a space heater operates to heat a room, heated air from the heat exchanger heated by the exhaust gases from the burner is circulated in the room by a convention fan to heat the air in the room up to a desired temperature. The space heater has a room temperature sensor (room temperature detecting means) for detecting the temperature of the air in the room, and a room temperature setting means for setting a target room temperature to a desired temperature. The space heater performs a temperature control process for determining an amount of combustion (an amount of heat) in the burner based on the difference between the room temperature detected by the room temperature sensor and a target room temperature set by the room temperature setting means. The temperature control process thus performed prevents the fuel from being combusted by the burner in excess of a determined amount of combustion and hence prevents the room temperature from being unduly increased. Therefore, an undesirably excessive consumption of the fuel by the burner can suppressed, and at the same time a comfortable room temperature can be achieved.
In cold climates where the outdoor temperature is very low, when the space heater is turned off, the indoor temperature tends to drop to such a low level that indoor facilities such as water supply pipes and aquariums may be frozen.
In order to prevent those indoor facilities from frozen, the space heater may be provided with a freeze prevention mode control means for forcibly starting to operate the space heater in a warming mode, i.e., a freeze prevention mode, when the room temperature falls below a freeze temperature for the indoor facilities while the space heater is being turned off or in a timer-controlled standby mode. The room temperature setting means may be operated by the user to set a freeze prevention temperature to any desired temperature.
In the freeze prevention mode, as with the normal warming mode, the temperature control process is carried out to determine an amount of combustion in the burner based on the difference between the room temperature detected by the room temperature sensor and a freeze prevention temperature selected by the user for thereby minimizing the amount of the consumed fuel while preventing the indoor facilities from being frozen.
The freeze prevention temperature that is set in the freeze prevention mode may be a temperature for preventing the indoor facilities from being frozen with a small amount of heat, and is set to a value which is lower than the temperature that is set in the normal warming mode. Since the freeze prevention mode is initiated when the detected room temperature drops below the freeze prevention temperature that is set by the user and thereafter the temperature control process is carried out, the difference between the freeze prevention temperature and the detected room temperature is small. Therefore, the amount of combustion in the burner in the temperature control process is small. When the space heater operates in the freeze prevention mode, the temperature of the heat exchanger itself is often considerably low because the heat exchanger has been cooled to a very low temperature by the air in the room. If the heat exchanger thus cooled is continuously heated by the burner which is controlled for the low amount of combustion, then moisture condensation occurs in the heat exchanger, shortening the service life of the heat exchanger.